| 研究生: |
黃婷卉 Huang, Ting-Hui |
|---|---|
| 論文名稱: |
土石流發生降雨特性之研究-以陳有蘭溪流域為主 Characteristics of Rains Triggering Debris Flows in the Watershed of Chenyoulen Stream |
| 指導教授: |
詹錢登
Jan, Chyan-Deng |
| 學位類別: |
碩士 Master |
| 系所名稱: |
工學院 - 水利及海洋工程學系 Department of Hydraulic & Ocean Engineering |
| 論文出版年: | 2003 |
| 畢業學年度: | 91 |
| 語文別: | 中文 |
| 論文頁數: | 88 |
| 中文關鍵詞: | 土石流 、降雨參數 、雨場分割方法 、警戒模式 、土石流發生機率 |
| 外文關鍵詞: | occurrence probability, warning model, rainfall parameter, definition of rainfall event, debris flow |
| 相關次數: | 點閱:108 下載:9 |
| 分享至: |
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台灣地區因為地形陡峭、地質破碎、豪雨集中,加上山坡地之過量開發,因此經常發生土石流災害。921集集大地震後,大量的鬆散土石,更增加了土石流發生的頻率與規模,尤其以中部重建區所發生的土石流災害最為嚴重。因此,如何發展土石流預報或預警系統,並提高其準確度,以減少人民生命財產的損失,為當前土石流災害防治工作的重要課題。
形成土石流的三個基本條件是豐富的鬆散土石、陡峻的坡度及大量的水源。對同一條土石流溝的集水區而言,地文、地形及土壤條件在一定正常的期間內可視為相對穩定且變化不大,但集水區內的降雨條件卻有很大的變化。台灣地區雨量豐沛且集中,土石流的發生和降雨有很密切的關係。若能分析出降雨條件在土石流集水區內的變化規律和發展趨勢,就有可能利用降雨條件作出土石流的預報及預警工作。目前國內土石流警戒區域的劃分與警戒基準值的訂定係採用有效降雨強度與有效累積雨量作為評估指標,經多次應用的結果發現,現在所使用的模式準確度不甚理想,仍需進行改善。
本文收集了國內外各種土石流發生降雨警戒值模式,檢討各模式之適用性,依據選用之降雨參數(降雨強度I、降雨延時T、累積雨量R及前期降雨量P)的差異,將土石流發生降雨警戒值模式分成五種類型:I-R類型、I-T類型、R-T類型、I-P類型及其他類型。本研究發現,多數研究者在處理降雨資料時所採用之雨場分割方法並不一致,若以前人曾採用的四種雨場分割方法來劃定一場連續降雨,雨場分割方法對降雨參數的計算影響相當大,亦會造成降雨警戒模式上之誤差。為改善四種雨場分割方法的缺點,本文另外提出兩種改善後的雨場分割方法與水保局目前所採用的雨場分割方法,針對降雨參數與土石流發生降雨警戒模式進行比較分析,並建議採用降雨強度與總有效累積雨量為指標之I-Rt模式。為了簡便起見,本文建議可採用單日有效累積雨量Rd加上前期雨量P的方法來估算總有效累積雨量。此外,考慮土石流發生在地文及水文條件上之不確定性,本文亦提出機率式土石流發生降雨警戒值模式,可提供土石流警戒區域的劃分與警戒基準值之參考。
Taiwan has highly steep topography, broken geological conditions, concentrated rainstorms, and over developed hillsides, and these have frequently resulted debris-flow hazards. After a severe earthquake of 7.3 Richard scale at Central Taiwan on November 21, 1999, a large amount of loose soils on hillsides largely increase debris-flow occurrence frequency and magnitude , especially in Central Taiwan. Therefore, it is important to develop accurate debris-flow forecast or warning systems for reducingthe lose of human lives and properties.
Three basic conditions for debris-flow occurrence are the abundant loose soils, the steep slope, and the large amount of water. For a specified watershed of a debris-flow gully, the changes of the topographical and geological conditions as well as the loose soil conditions in a period of normal time are negligible compared with the change of rainfall. Taiwan has heavy and concentrated rainfall, so occurrences of debris flows in Taiwan are always closely related with rainfall characteristics. If one can analyze the rainfall and its tendency, it is possible to predict debris flow occurrence potential based on the rainfall condition. Even though the effective rainfall intensity and the effective accumulated rainfall as well as other rainfall factors have been used to be rainfall indexes for debris flow prediction in Taiwan, there are still large rooms to be improved according to practical application experiences.
This paper collects various rainfall-based debrisflow occurrence models, compares the differences and the suitability of the models, and then proposes an improved method for the prediction/warning of debris-flow occurrence. The common rainfall parameters used in debris-flow warning models are the rainfall intensity I, rainfall duration T, accumulated rainfall R and previous accumulated rainfall P. Based on the four rainfall parameters, debris-flow occurrence warning models could be classified into five categories: I-R model, I-T model, R-T model, I-P model and others. It has been found that there is inconsistent in defining a rainfall event used in analyzing debris-flow initiation. There are about four difference definitions of a rainfall event used by previous debris-flow investigators. Four kinds of rainfall-event definitions have been used and compared to analyze the rainfall parameters. The results show that different rainfall-event definitions would result different rainfall parameters, and their differences are very large. The paper proposed another two methods to define a rainfall event that would be more suitable for analyzing debris-flow initiation. The rainfall parameters obtained by the proposed method are also compared with that obtained by the present method used by the Soil and Water Conservation Bureau (SWCB), Council of Agriculture in Taiwan This paper also proposes a probability-based debris flow rainfall warning model.
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